In the early nineteen fifties, a new organometallic compound was synthesized, originally named dicyclopentadienyl iron. Kealy, T. J. and P. L. Paulson, Nature 168, 1039 (1951). Soon after publication of the original papers describing this compound, its correct structure was proposed, Fischer, E. O. and W. Pfab, Z. Naturaforsch. 7b, 377 (1952), its aromaticity proved, hence the name "ferrocene", Rosenblum, M. et al., J. Am. Chem. Soc. 74, 3458 (1952) and the first dicyclopentadienyl complexes or other transition metals were synthesized (Fischer, E. O. and H. P. Fritz, Adv. Inorg. Chem. Radiochem. 1, 56 (1959).
Since then, there has been increasing interest in synthesis and properties of stacked columns of organometallic compounds. Among these materials are the multidecked nickelocenes in which two nickel atoms are located between three mutually parallel cyclopentadienyl rings, Werner, H. Angnew Chemie. Int. Ed. 16, 1-64 (1977). Columnar organometallics also include the related planar iron, cobalt, and nickel complexes of heterocyclic boron compounds such as the triborales, Beer, D. C. et al. J. Am. Chem. Soc. 95, 3046-3048 (1973) and diborales, Siebert, W. Agnew Chemie Int. Ed. 24, 943-958 (1985). Recently, a cobaltocenium salt of helicene, a helical structure of fused benzene rings capped by unsaturated 5-membered rings has been synthesized. Sudhakar et al. J. Am. Chem. Soc. 108, 2790-2791 (1986).
As exemplified by the iodine-doped phthalocyanate-metalloxanes, Hanack. M., Chimia, 37: 238 (1983) and the polyferrocenylenes, Neuse U.S. Pat. No. 3,437,634, polymeric organometallic complexes yield materials with unusual properties.